This invention is directed to the field of networking devices, such as networking appliances coupled to a home network.
The Home Phone-Line Networking Alliance (HomePNA) is an industry-sponsored Special Interest Group creating a standard for networking of information appliances via the telephone lines within a home or other building. The network communications occur at a high frequency, so that they do not interfere with conventional telephone conversations or digital subscriber line (DSL) communications. There is currently a HomePNA 1.0 standard that operates at approximately 1 Mbps (Mega-bits per second). The HomePNA is working to establish a 2.0 standard that operates at approximately 10 Mbps. Devices that operate according to the 1.0 standard are often referred to as version 1 or V1.x devices, and devices that operate according to the 2.0 standard are often referred to as version 2 or V2.x devices.
Both the 1.0 and 2.0 HomePNA standards operate according to Ethernet principles, as described in the IEEE 802.3 standard, which is incorporated herein by reference. A well-known principle of the 802.3 standard is known as CSMA/CD, which stands for Carrier Sense Multiple Access/Collision Detect. Essentially, CSMA/CD enables any device to transmit, as long as no other devices are transmitting. Each device, prior to transmitting, checks to see if the medium is free (carrier sense) and only transmits if the device senses that the medium is free. If two or more devices sense the medium is free, and transmit simultaneously, a collision is detected and the devices back off according to a predetermined protocol. The devices will then subsequently retry to transmit, according to the protocol.
One of the requirements of V2.x devices is that they are compatible with V1.x devices, also referred to as xe2x80x9clegacyxe2x80x9d devices. Thus, if a user has a first computer operating according to the V1.x standard, and a second computer operating according to the V2.x standard, the second computer must act in a way that is compatible with the first computer if both computers are active and coupled to a common network. This compatibility includes two primary requirements. First, the V2.x device must be able to communicate with the V1.x device. Second, the V2.x device must operate in a way that enables the V1.x device to recognize that the V2.x device is operating, even if the V2.x device is communicating with another V2.x device.
The conventional view is that when there is a mixed version HPNA system (i.e., at least one V1.x device and at least one V2.x device), when node detection occurs and a V2.x device detects the presence of a V1.x device, the entire link will drop back to the V1.x rate. This drop back procedure is inefficient since it will cause communication between two V2.x devices to occur at the V1.x rate. However, the conventional view is that the drop back procedure is necessary so that V1.x devices can sense the communication between the two V2.x devices, and not erroneously disrupt the communication by attempting to transmit. This approach is inadequate because it does not take advantage of the V2.x capabilities, and instead acts as if the entire network is made of V1.x nodes.
An alternative approach employs separate frequency spectra for each type of device when in a mixed-mode topology. According to this approach, an advanced (e.g. V2.x) device will communicate with other advanced devices at one (e.g. higher) frequency, and will communicate with legacy (e.g. V1.x) devices at a separate (e.g. lower) frequency. This alternative approach is not adequate because at higher frequencies significant design challenges are made even more difficult. Also, this approach leads to higher cost system designs. At higher frequencies, some of the design challenges are that Near End Crosstalk (NEXT) is more pronounced, line attenuation gets worse, spectral nulls become deeper and wider, and the technical specifications required to introduce product into the consumer marketplace based on FCC Part 15 requirements become more stringent. Due to these technical constraints, the conventional wisdom is that the spectral sharing concept, e.g. where legacy and advanced devices share the same frequency band, is the preferred approach.
What is needed is a system that allows for compatibility of future versions of home networking appliances with older versions, without causing the entire network to drop back to the speed of the older version, and without the design complexity of the high frequency alternative.
In a first embodiment according to the invention, a networking device includes a legacy preamble injector adapted to insert a legacy preamble based on an indication that a legacy device is coupled to a common network. The legacy preamble injector may be adapted to insert the legacy preamble if the legacy device is a target device for communication from the network appliance. Alternatively, the device may be adapted to output a payload portion at a native rate, for example, if the legacy device is not the target.
An exemplary embodiment is a Home Phone Line Network Alliance (HomePNA) system, including a telephone line network, and a plurality of devices coupled by the network. The plurality of devices may include at least one V2.x device and at least one V1.x device. According to the invention, the at least one V2.x device is adapted to recognize the presence on the network of the at least one V1.x device, and to modify a transmission frame format based on this recognition.
In an alternative embodiment according to the invention, a method of communicating on a telephone line network includes the steps of recognizing the presence on the network of a relatively low speed device, and injecting a preamble at a rate corresponding to the relatively low speed device. According to this method, a payload portion at the rate corresponding to the relatively low speed device may be transmitted if the relatively low speed device is a target device. Alternatively, a payload portion at a rate corresponding to a relatively high speed device may be transmitted if a relatively high speed device is a target device.
A networking appliance according to the invention is thus adapted to send out a frame that allows legacy terminals to demodulate valid preamble. This allows legacy terminals to maintain carrier sense for the duration of the packet. In one embodiment, this is accomplished by adding a valid legacy preamble followed by advanced native rate format and payload data in a heterogeneous network. While data throughput may be degraded when compared to that of a homogenous advanced network, the end user will experience greater data throughput than can be expected in a legacy-only topology or the full fallback implementation in a heterogeneous topology.
These and other advantages of the invention will be apparent to one of skill in the art upon review of the following detailed description in light of the drawing, wherein:
FIG. 1 is a simplified block diagram showing an exemplary multiplexing scheme wherein both advanced and legacy device paths are considered;
FIG. 2 is a simplified block diagram of the multiplexing scheme of FIG. 1, when a legacy mode is active;
FIG. 3 is a simplified block diagram of an exemplary hardware solution for isolated heterogeneous networks; and
FIG. 4 provides an exemplary frame format for use in a mixed mode topology according to the invention.